1. Field of the Invention
The present invention relates to a control system for an internal combustion engine, and particularly, to a system for controlling an internal combustion engine according to a pressure in the cylinder detected by a cylinder pressure sensor.
2. Description of the Related Art
Japanese Patent Laid-open No. 2004-100566 (JP '566) discloses a fuel injection control apparatus in which the cylinder pressure (pressure in the combustion chamber) is detected by a cylinder pressure sensor, and a fuel injection amount, a fuel injection timing, and the like, are controlled according to the detected cylinder pressure. According to the disclosed apparatus, the crank angle Cmax at which the cylinder pressure reaches a maximum value is detected, and the fuel injection timing is corrected so that the detected crank angle Cmax coincides with a target value which is previously set according to the engine operating condition.
If the internal combustion engine is a diesel engine, an actual ignition timing changes depending on the cetane number of the fuel being used, even if the fuel injection timing is the same. Therefore, the control used by the above-described conventional apparatus is effective when the combustion characteristic of fuel changes.
However, a specific method for correcting the fuel injection timing is not shown in JP '566. For example, if the cylinder pressure is to be detected during comparatively short periods of time and control is to be performed based on the detection results, the calculation load on the control apparatus increases. Accordingly, correction of the fuel injection timing must be performed without excessively increasing the calculation load on the control apparatus. However, the apparatus shown in JP '566 is not configured in contemplation of such a situation, thereby delaying performance of the control.